The present invention relates to a lignocellulose-containing material obtainable by treating lignocellulose A with a binder B as defined in the claims.
The present invention furthermore relates to moldings comprising a lignocellulose-containing material, a process for the production of the lignocellulose-containing material, a process for the production of moldings using the lignocellulose-containing material, the use of the lignocellulose-containing material for the production of moldings and the use of the moldings for the production of pieces of furniture and of packaging materials, in house construction or in interior finishing or in motor vehicles.
Materials based on lignocellulose are known. Important examples of lignocellulose-containing materials are wood parts, such as wood layers, wood strips, wood chips or wood fibers, it also being possible for the wood fibers to originate from wood fiber-containing plants, such as flax, hemp, sunflowers, topinambur or rape. Starting materials for such wood parts or wood particles are usually timbers from the thinning of forests, residual industrial timbers and used woods and wood fiber-containing plants.
The processing to give the desired lignocellulose-containing materials, such as wood particles, is effected by known processes, cf. for example M. Dunky, P. Niemt, Holzwerkstoffe and Leime, pages 91-156, Springer Verlag, Heidelberg, 2002.
Lignocellulose-containing moldings, also referred to here as wood-base materials in the case of wood as lignocellulose, are an economical and resource-protecting alternative to solid wood of considerable importance in particular in furniture construction and as building materials. As a rule, wood layers of different thickness, wood strips, wood chips or wood fibers from various timbers serve as starting materials for wood-base materials. Such wood parts or wood particles are usually compressed at elevated temperature with natural and/or synthetic binders and, if appropriate, with addition of further additives to give board- or strand-like wood-base materials. Examples of such lignocellulose-containing moldings or wood-base materials are medium density fiber boards (MDF), woodchip materials, such as particle boards and coarse particle boards (OSB, oriented strand board), plywood, such as veneer plywood, and glued wood.
Binders used are as a rule formaldehyde-containing binders, for example urea-formaldehyde resins or melamine-containing urea-formaldehyde resins. The resins are prepared by polycondensation of formaldehyde with urea and/or melamine. The use of such formaldehyde resins can result in the presence of free formaldehyde in the finished wood-base material. Additional formaldehyde may be liberated by hydrolysis of the polycondensates. The free formaldehyde present in the wood-base material and the formaldehyde liberated by hydrolysis during the life of the wood-base material can be released to the environment.
Above certain limits, formaldehyde may cause allergies and irritation of skin, respiratory tract or eyes in humans. The reduction of the formaldehyde emission in components, especially in the interior, is therefore an important challenge.
Certain formaldehyde-free aqueous binders—inter alia for wood fibers—based on polymers of ethylenically unsaturated carboxylic acids are described in the prior art:
WO 97/31059 A1 (BASF Aktiengesellschaft) describes the use of a formaldehyde-free, aqueous binder comprising A) polycarboxylic acid and B) an alkanolamine having at least two hydroxyl groups as a binder for fibers, shavings or chips for the production of moldings. In the examples, an aqueous solution of an 80 acrylic acid/20 maleic acid copolymer is described as component A) and triethanolamine is described as component B) and the use of the corresponding binder for the production of wood particle boards is described.
DE 102 53 498 A1 (BASF Aktiengesellschaft) describes an aqueous polymer dispersion which is obtainable by aqueous emulsion polymerization of, for example, acrylate and styrene monomers in the presence of a polymer A2, for example based on a copolymer of acrylic acid/maleic anhydride/unsaturated amine component. The aqueous polymer dispersion thus obtainable is used for structural wood gluing.
WO 2006/82223 A1 (BASF Aktiengesellschaft) describes a certain aqueous polymer dispersion obtainable by free radical emulsion polymerization, formed, for example, by polymerization of the monomers methacrylic acid, N-methylolacrylamide, methyl methacrylate, styrene and n-butyl acrylate. Use of such polymer dispersions as binders for cellulosic fibers for the production of filter materials or as base paper for decorative sheets is claimed.
WO 2007/122089 A1 (BASF Aktiengesellschaft) describes an aqueous polymer composition which is obtainable by free radical aqueous emulsion polymerization of, for example, acrylic acid and acrylate and styrene monomers in the presence of a polymer A2, for example based on an acrylic acid homopolymer. The aqueous polymer dispersion thus obtainable is used in the examples as a binder for pressed test specimens comprising hemp/flax fiber mats.
The binders described in the prior art may well be formaldehyde-free but still leave room for improvements, for example with regard to mechanical load capacities (for example transverse tensile strength) or behavior toward water (for example swelling) of the moldings produced with them.